Resonant helicity mixing of electromagnetic waves propagating through matter

TL;DR

This paper demonstrates that index-matched media can resonantly induce helicity mixing in electromagnetic waves, revealing new insights into scattering phenomena and challenging previous assumptions about passive scatterers.

Contribution

It provides a general proof of the non-existence of passive antidual scatterers and links refractive index matching to helicity flipping and resonant mixing in electromagnetism.

Findings

Passive antidual scatterers cannot exist.

Refractive index matching enables efficient helicity flipping.

Index-matched media induce resonant helicity mixing.

Abstract

Dual scatterers preserve the helicity of an incident field, whereas antidual scatterers flip it completely. In this setting of linear electromagnetic scattering theory, we provide a completely general proof on the non-existence of passive antidual scatterers. However, we show that scatterers fulfilling the refractive index matching condition flip the helicity of the fields very efficiently without being in contradiction with the law of energy conservation. Moreover, we find that this condition is paired with the impedance matching condition in several contexts of electromagnetism and, in particular, within Fresnel's and Mie's scattering problems. Finally, we show that index-matched media induce a resonant helicity mixing on the propagating electromagnetic waves. We reach to this conclusion by identifying that the refractive index matching condition leads to the phenomenon of avoided level-crossing. Our contribution not only closes a historical discussion within the Nanophotonics community, but also opens up new possibilities in the fields of Metamaterials and Particle Physics.